1. Field of the Invention
This invention relates to a video camera (a still/movie video camera) in which exposure conditions are decided upon performing photometry of a subject using a video signal obtained from a solid-state electronic image sensing device, and a method of photometry used in this video camera. More particularly, the invention relates to a video camera for performing split photometry and a method of split photometry used in this video camera.
The invention relates further to an image pick-up apparatus for photographing a subject using a solid-state electronic image sensing device and outputting a video signal or image data representing the subject, as in the manner of a video camera, a method of photometry and a method of focusing control used in this apparatus, as well as an image pick-up method.
2. Description of the Background Art
Photometry is required in order to determine exposure conditions in a camera having an automatic exposure (so-called "AE") function. In a case where the luminance of a subject in a photographic area differs greatly from one location to another, as in a case where photography is performed under backlighted conditions, it is necessary to obtain a photometric value for every location on the subject (every portion thereof) and carry out exposure control conforming to the photometric values. To achieve this, it is known to use so-called split photometry, in which the photographic area is subdivided into a plurality of small areas and a photometric value is obtained for each small area.
Split photometry is performed using a photometric element, which is specifically used for split photometry, having a plurality of subdivided light-receiving areas. When this special photometric Element is used, however, a problem encountered is that the split photometric areas are fixed and cannot be changed as necessary.
Accordingly, it may be considered to perform split photometry utilizing a video signal outputted by a solid-state electronic image sensing device with which a video camera is equipped. In such an arrangement, however, a detecting circuit and A/D converter are required for each of the plurality of split photometric areas. This is an impediment in terms of obtaining a camera of small size, little power consumption and low cost. If photometric processing regarding one split photometric area is performed at intervals of one frame or one field, one set of the detector circuit and A/D converter will suffice. However, this will require more time for photometric processing and, hence, a longer period of time before actual photography can be performed.
On the other hand, in an image pick-up apparatus such as a video camera, photography of a subject is performed using a solid-state electronic image pick-up device (a CCD, for example). A solid-state electronic image pick-up device is capable of providing information indicative of the subject on a pixel-by-pixel basis. With a solid-state electronic image pick-up device having an array of 1280 pixels in the horizontal direction and 1024 pixels in the vertical direction, as much as about 1,300,000 items of information can be provided.
In a video camera equipped with a solid-state electronic image sensing device and adapted to obtain a video signal of a photographic subject, consideration may be given to a method of obtaining photometric values by integrating the video signal output from the solid-state electronic image sensing device over an appropriate photometric area as well as to a method of controlling the focusing of an image pick-up lens by integrating the video signal over an appropriate rangefinding area. In order to improve accuracy in these methods, the general practice is to exclude portions in the photographic area in which the video signal saturates, if such portions exist.
Since a solid-state electronic image sensing device provides an item of information for each and every pixel, it is preferred in these methods of performing photometry and focusing control using a video signal that the discrimination of portions in which the video signal saturates, as well as the exclusion of these portions, be carried out for each and every pixel.
However, executing the processing of the video signal or image data on a pixel-by-pixel basis is impractical since such processing is difficult for a small-size microcomputer even when storage of the signal or data in an image memory is considered.